[PATCH v7 1/1] ldconfig: add --install option
Adhemerval Zanella Netto
adhemerval.zanella@linaro.org
Tue Jul 7 17:17:35 GMT 2026
On 30/06/26 18:28, DJ Delorie wrote:
>
> Add --install option, which copies a pre-built ld.so.cache into place,
> honoring the cache and root options and defaults. This gives the user
> a canonical "correct" way to install a pre-built cache without risk
> of a program trying to load a partially-written file.
>
> Co-authored-by: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
This version looks good to me, thanks.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
>
> --- >8 ---
>
> Changes since v6:
> - split install_cache_file into separate function
> - preserve errno across unlink/close
> - don't use errno from
>
> Changes since v5:
> - Fixed style issues
> - Make counters ssize_t
> - Fix write count accumulation logic
> - additional error checks
>
> Changes since v4:
> - Added testcase
> - Fix open mode
>
> Changes since v3:
> - initialize w because some compilers can't tell initialization
> isn't needed.
>
> Changes since v2:
> - removed "rename if possible" option to avoid removing source file.
> We always copy now.
> ---
> NEWS | 2 +
> elf/Makefile | 6 ++
> elf/ldconfig.c | 162 +++++++++++++++++++++++++++++++++++-
> elf/tst-ldconfig-install.sh | 125 ++++++++++++++++++++++++++++
> 4 files changed, 293 insertions(+), 2 deletions(-)
> create mode 100644 elf/tst-ldconfig-install.sh
>
> diff --git a/NEWS b/NEWS
> index f9d90c5194..e30b7a5f76 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -37,6 +37,8 @@ Major new features:
> status via prctl syscall. This prevents disabling or corrupting GCS
> shadow stack during runtime.
>
> +* Pre-built ld.so.cache files can be installed with ldconfig.
> +
> Deprecated and removed features, and other changes affecting compatibility:
>
> * Although malloc and related functions currently return pointers
> diff --git a/elf/Makefile b/elf/Makefile
> index 789c504da9..3479450191 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -718,6 +718,7 @@ tests-special += $(tests-execstack-special-$(have-z-execstack))
> ifeq ($(run-built-tests),yes)
> tests-special += \
> $(objpfx)tst-ldconfig-X.out \
> + $(objpfx)tst-ldconfig-install.out \
> $(objpfx)tst-ldconfig-p.out \
> $(objpfx)tst-ldconfig-soname.out \
> $(objpfx)tst-rtld-help.out \
> @@ -2833,6 +2834,11 @@ $(objpfx)tst-ldconfig-X.out : tst-ldconfig-X.sh $(objpfx)ldconfig
> '$(run-program-env)' > $@; \
> $(evaluate-test)
>
> +$(objpfx)tst-ldconfig-install.out : tst-ldconfig-install.sh $(objpfx)ldconfig
> + $(SHELL) $< '$(common-objpfx)' '$(test-wrapper-env)' \
> + '$(run-program-env)' > $@; \
> + $(evaluate-test)
> +
> $(objpfx)tst-ldconfig-p.out : tst-ldconfig-p.sh $(objpfx)ldconfig
> $(SHELL) $< '$(common-objpfx)' '$(sysconfdir)' '$(test-wrapper-env)' \
> '$(run-program-env)' > $@; \
> diff --git a/elf/ldconfig.c b/elf/ldconfig.c
> index 1ea55400f3..a39f3ecfcd 100644
> --- a/elf/ldconfig.c
> +++ b/elf/ldconfig.c
> @@ -109,6 +109,9 @@ static int opt_manual_link;
> /* Should we ignore an old auxiliary cache file? */
> static int opt_ignore_aux_cache;
>
> +/* Install a pre-existing cache file instead of generating a new one. */
> +static int opt_install;
> +
> /* Cache file to use. */
> static char *cache_file;
>
> @@ -141,6 +144,7 @@ static const struct argp_option options[] =
> { NULL, 'l', NULL, 0, N_("Manually link individual libraries."), 0},
> { "format", 'c', N_("FORMAT"), 0, N_("Format to use: new (default), old, or compat"), 0},
> { "ignore-aux-cache", 'i', NULL, 0, N_("Ignore auxiliary cache file"), 0},
> + { "install", 'I', NULL, 0, N_("Install pre-existing cache file"), 0},
> { NULL, 0, NULL, 0, NULL, 0 }
> };
>
> @@ -209,6 +213,9 @@ parse_opt (int key, char *arg, struct argp_state *state)
> else if (strcmp (arg, "new") == 0)
> opt_format = opt_format_new;
> break;
> + case 'I':
> + opt_install = 1;
> + break;
> default:
> return ARGP_ERR_UNKNOWN;
> }
> @@ -1041,6 +1048,155 @@ search_dirs (void)
> }
> }
>
> +static void
> +install_cache_file (const char *source_arg)
> +{
> + int e;
> +
> + if (source_arg == NULL)
> + error (EXIT_FAILURE, 0, _("Missing source file name"));
> +
> + const char *source = (opt_chroot
> + ? chroot_canon (opt_chroot, source_arg)
> + : source_arg);
> + if (source == NULL)
> + error (EXIT_FAILURE, errno, _("Can't find %s"), source_arg);
> +
> + int src_fd = open (source, O_RDONLY);
> + if (src_fd < 0)
> + error (EXIT_FAILURE, errno, _("Can't open %s"), source);
> +
> + char *dest = xmalloc (strlen (cache_file) + 1 + 1);
> +
> + /* This matches the temp file created by cache.c, and should be
> + on the same filesystem as the cache file. */
> + sprintf (dest, "%s~", cache_file);
> + int dest_fd;
> +
> + struct stat st;
> + if (fstat (src_fd, &st) < 0)
> + error (EXIT_FAILURE, errno, _("Can't stat %s"), source);
> +
> + char buf[512];
> + ssize_t r, w = 0, sz = 0;
> + char *bp = buf;
> +
> + /* Read the first part of the file and verify it looks
> + reasonable. */
> + while (sz < sizeof (buf)
> + && (r = read (src_fd, bp, sizeof (buf) - sz)) > 0)
> + {
> + sz += r;
> + bp += r;
> + }
> + if (r < 0)
> + error (EXIT_FAILURE, errno, _("Error reading file %s"), source);
> +
> + if (! ((sz >= sizeof (CACHEMAGIC)
> + && memcmp (buf, CACHEMAGIC,
> + sizeof (CACHEMAGIC) - 1) == 0)
> + || (sz >= sizeof (CACHEMAGIC_NEW)
> + && memcmp (buf, CACHEMAGIC_NEW,
> + sizeof (CACHEMAGIC_NEW) - 1) == 0)))
> + {
> + error (EXIT_FAILURE, 0,
> + _("File %s does not look like an ld.so.cache file"),
> + source);
> + }
> +
> + /* Now write that first part out. */
> + dest_fd = open (dest, O_CREAT|O_WRONLY|O_TRUNC|O_NOFOLLOW,
> + S_IRUSR|S_IWUSR);
> + if (dest_fd < 0)
> + error (EXIT_FAILURE, errno, _("Can't create %s"), dest);
> +
> + r = sz;
> + bp = buf;
> + while (r > 0 && (w = write (dest_fd, bp, r)) > 0)
> + {
> + r -= w;
> + bp += w;
> + }
> + if (w < 0)
> + {
> + e = errno;
> + unlink (dest);
> + close (dest_fd);
> + error (EXIT_FAILURE, e, _("Error writing file %s"), dest);
> + }
> +
> + /* At this point, sz contains the number of bytes copied so far.
> + Copy the rest of the file. */
> + while ((r = read (src_fd, buf, sizeof(buf))) > 0)
> + {
> + bp = buf;
> + while (r > 0 && (w = write (dest_fd, bp, r)) > 0)
> + {
> + bp += w;
> + r -= w;
> + sz += w;
> + }
> + if (w <= 0)
> + break;
> + }
> + if (r < 0)
> + {
> + e = errno;
> + unlink (dest);
> + close (dest_fd);
> + error (EXIT_FAILURE, e, _("Error reading file %s"), source);
> + }
> + if (w < 0)
> + {
> + e = errno;
> + unlink (dest);
> + close (dest_fd);
> + error (EXIT_FAILURE, e, _("Error writing file %s"), dest);
> + }
> +
> + close (src_fd);
> +
> + /* Make sure we copied it all. */
> + if (sz < st.st_size)
> + {
> + unlink (dest);
> + close (dest_fd);
> + error (EXIT_FAILURE, 0, _("Unable to copy file %s to %s"),
> + source, dest);
> + }
> +
> + /* Make sure user can always read the cache file */
> + if (fchmod (dest_fd, S_IROTH|S_IRGRP|S_IRUSR|S_IWUSR))
> + {
> + e = errno;
> + unlink (dest);
> + close (dest_fd);
> + error (EXIT_FAILURE, e,
> + _("Changing access rights of %s to %#o failed"), dest,
> + S_IROTH|S_IRGRP|S_IRUSR|S_IWUSR);
> + }
> +
> + if (fsync (dest_fd) != 0)
> + {
> + e = errno;
> + unlink (dest);
> + close (dest_fd);
> + error (EXIT_FAILURE, e, _("Writing to %s failed"), dest);
> + }
> +
> + if (rename (dest, cache_file) < 0)
> + {
> + e = errno;
> + unlink (dest);
> + close (dest_fd);
> + error (EXIT_FAILURE, e, _("Can't rename %s to %s"),
> + dest, cache_file);
> + }
> +
> + if (close (dest_fd) != 0)
> + error (EXIT_FAILURE, errno, _("Writing to %s failed"), dest);
> + exit (0);
> +}
>
> int
> main (int argc, char **argv)
> @@ -1060,8 +1216,8 @@ main (int argc, char **argv)
> argp_parse (&argp, argc, argv, 0, &remaining, NULL);
>
> /* Remaining arguments are additional directories if opt_manual_link
> - is not set. */
> - if (remaining != argc && !opt_manual_link)
> + and opt_install are not set. */
> + if (remaining != argc && !opt_manual_link && !opt_install)
> {
> int i;
> for (i = remaining; i < argc; ++i)
> @@ -1157,6 +1313,8 @@ main (int argc, char **argv)
> exit (0);
> }
>
> + if (opt_install)
> + install_cache_file (argv[remaining]);
>
> if (opt_build_cache)
> init_cache ();
> diff --git a/elf/tst-ldconfig-install.sh b/elf/tst-ldconfig-install.sh
> new file mode 100644
> index 0000000000..550281c7ab
> --- /dev/null
> +++ b/elf/tst-ldconfig-install.sh
> @@ -0,0 +1,125 @@
> +#!/bin/sh
> +# Test that ldconfig --install installs a pre-built cache file.
> +# Copyright (C) 2026 Free Software Foundation, Inc.
> +# This file is part of the GNU C Library.
> +
> +# The GNU C Library is free software; you can redistribute it and/or
> +# modify it under the terms of the GNU Lesser General Public
> +# License as published by the Free Software Foundation; either
> +# version 2.1 of the License, or (at your option) any later version.
> +
> +# The GNU C Library is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> +# Lesser General Public License for more details.
> +
> +# You should have received a copy of the GNU Lesser General Public
> +# License along with the GNU C Library; if not, see
> +# <https://www.gnu.org/licenses/>.
> +
> +set -e
> +
> +common_objpfx=$1
> +test_wrapper_env=$2
> +run_program_env=$3
> +
> +testroot="${common_objpfx}elf/tst-ldconfig-install-directory"
> +cleanup () {
> + rm -rf "$testroot"
> +}
> +trap cleanup 0
> +
> +rm -rf "$testroot"
> +mkdir -p "$testroot/etc"
> +
> +ldconfig="${common_objpfx}elf/ldconfig"
> +run_ldconfig () {
> + ${test_wrapper_env} ${run_program_env} "$ldconfig" "$@"
> +}
> +
> +errors=0
> +fail () {
> + echo "error: $1"
> + errors=1
> +}
> +
> +# Build a pre-built cache to install.
> +source="$testroot/prebuilt-ld.so.cache"
> +mkdir -p "$testroot/lib"
> +run_ldconfig -X -f /dev/null -C "$source" "$testroot/lib"
> +test -r "$source" || fail "ldconfig did not create the pre-built cache"
> +
> +# Pad the source past the 512-byte internal copy buffer so that the multi-block
> +# copy path is exercised, while leaving the cache magic at the start intact.
> +dd if=/dev/zero bs=1024 count=4 >> "$source" 2>/dev/null
> +
> +dest="$testroot/etc/ld.so.cache"
> +temp="$dest~"
> +
> +run_ldconfig --install -f /dev/null -C "$dest" "$source"
> +
> +# The destination must exist and be byte-identical to the source.
> +if test -r "$dest"; then
> + if cmp -s "$source" "$dest"; then
> + echo "info: installed cache matches the source"
> + else
> + fail "installed cache differs from the source"
> + fi
> +else
> + fail "destination cache file was not created"
> +fi
> +
> +# The temporary file used during the atomic rename must not be left behind.
> +if test -e "$temp"; then
> + fail "temporary file $temp was left behind"
> +fi
> +
> +# The installed cache must be world-readable (0644).
> +if test -r "$dest"; then
> + mode=$(ls -l "$dest" | cut -c1-10)
> + case "$mode" in
> + (-rw-r--r--) echo "info: installed cache has expected permissions" ;;
> + (*) fail "installed cache has unexpected permissions: $mode" ;;
> + esac
> +fi
> +
> +# A second install over an existing cache must also succeed.
> +run_ldconfig --install -f /dev/null -C "$dest" "$source"
> +if cmp -s "$source" "$dest"; then
> + echo "info: re-install over an existing cache works"
> +else
> + fail "re-install produced a different cache"
> +fi
> +
> +# Error case: a source file that is not a cache must be rejected, and no
> +# destination must be produced.
> +rm -f "$dest"
> +notcache="$testroot/not-a-cache"
> +echo "this is not an ld.so.cache file" > "$notcache"
> +if run_ldconfig --install -f /dev/null -C "$dest" "$notcache" 2>"$testroot/err"; then
> + fail "ldconfig accepted a file that is not a cache"
> +else
> + if grep -q "does not look like an ld.so.cache file" "$testroot/err"; then
> + echo "info: non-cache source correctly rejected"
> + else
> + fail "unexpected error message for non-cache source"
> + cat "$testroot/err"
> + fi
> +fi
> +test -e "$dest" && fail "destination created from an invalid source"
> +
> +# Error case: a missing source argument must be diagnosed.
> +if run_ldconfig --install -f /dev/null -C "$dest" 2>"$testroot/err"; then
> + fail "ldconfig accepted --install without a source file"
> +else
> + grep -q "Missing source file name" "$testroot/err" \
> + || fail "unexpected error message for missing source"
> +fi
> +
> +# Error case: a nonexistent source must be diagnosed.
> +if run_ldconfig --install -f /dev/null -C "$dest" \
> + "$testroot/does-not-exist" 2>"$testroot/err"; then
> + fail "ldconfig accepted a nonexistent source file"
> +fi
> +
> +exit $errors
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